In cavity brick or block masonry construction, weep hole openings are left in mortar joints just above the flashing to allow both ventilation and drainage of the wall cavity between the exterior masonry and the interior wall. A weep hole opening is typically formed by the omission of mortar between two adjacent bricks or blocks. The weep hole opening provides ventilation and drainage to keep the wall cavity dry. Without adequate ventilation, dampness causes mildew and rot, which reduce the life of the structure.
Weephole openings vary considerably in size and shape dependent on the skill and care of the tradesmen and the type of brick and type of finishes being applied. A problem with weep hole openings situated close to ground level, as are common, is that they can become an entry for rodents and reptiles. Similarly, a problem with weep hole openings around windows or second floors is that they can provide an entry for insects. In particular, the weep hole opening leading to the wall cavity is an ideal home for bees, wasps and other insects, which themselves create food sources for other pests. Another problem associated with weep hole openings is that they provide an entry point for water, particularly during excessive rain or from garden sprinklers. Another problem with weep hole openings is that they can allow sparks and firebrands to penetrate a building.